Conventionally, addition polymers of cyclic olefins represented by norbornene polymers have been industrially used in the field of optical films and the like as an organic material being excellent in heat resistance and transparency. There have been various reports that such addition polymers of cyclic olefins can be produced by the addition polymerization of cyclic olefin monomer(s) using a catalyst containing transition metal compounds such as Ti, Zr, Cr, Co, Ni and Pd.
For example, the European Patent Publication No. 0445755 (Patent Document 1) reports that an addition homopolymer of norbornene having the number average molecular weight exceeding 1,000,000 can be produced by polymerizing a norbornene monomer alone by using a transition metal compound of elements belonging to five to ten groups of the periodic table as a main catalyst and methylaluminoxane (MAO) as a cocatalyst. However, polymerization of norbornene monomers containing polar groups which has higher difficulty in polymerization has not been conducted with this catalyst system, and there were concerns about the catalyst deactivation due to the influence of the polar group.
Meanwhile, U.S. Pat. No. 3,330,815 publication (Patent Document 2) discloses addition homopolymers of norbornene monomers containing polar groups and copolymers with norbornene using only dichlorobis(benzonitrile)palladium and allyl palladium chloride dimer as a catalyst. However, the patent has not reported an example where a polymer having a number average molecular weight exceeding 10,000. Also, the polymerization activity of the catalyst is low so that the production method was far from being an industrially useful method.
Moreover, Japanese Patent Publication No. 3678754 (WO96/37526; Patent Document 3) and JPA-2008-31304 publication (Patent Document 4) disclose a method for improving addition polymerization of a norbornene monomer alone containing polar group or copolymerization with norbornene. Though these methods improved both of polymerization activity and molecular weight of the obtained polymer by using a combination of allyl palladium chloride dimer with silver tetrafluoroborate and silver hexafluorophosphate as a catalyst, they only disclose copolymer having number average molecular weight less than 200,000 in examples and have not succeeded in producing copolymers having number average molecular weight of 200,000 or more which is required for mechanical properties to be developed to a practical level. In Table 1 of Patent Document 4, the number average molecular weight (Mn) entries and the weight average molecular weight (Mw) entries replace each other. It is obvious from that Mw/Mn values should be around 2.5, and it is clear that a copolymer having a number average molecular weight exceeding 200,000 did not exist if data in Table 1 are interpreted properly.
Contrary to these methods, International publication No. WO2006/064814 (US 2009/264608; Patent Document 5) discloses that addition copolymerization of norbornene containing polar group and norbornene can be efficiently performed by using compounds of transition metals belonging to eighth to tenth groups of the periodic table as a main catalyst in combination with a cocatalyst capable of producing a cationic transition metal compound through the reaction with the main catalyst to thereby obtain copolymers having high molecular weight. However, the norbornene compound disclosed by the publication has a structure wherein an ester group is directly introduced into a norbornene skeleton, and since the distance between the carbon-carbon double bonding site and the polar group is short, the norbornene compound easily forms coordinate bonding with a transition metal complex as a catalyst, resulting in catalyst deactivation. Accordingly, the method enables to produce a high molecular weight polymer by high activity in addition polymerization of norbornene alone. However, in case of using a norbornene monomer having a polar group, a copolymer having high molecular weight can be obtained but the catalyst activity of the copolymer was low.
As one of the methods to prevent the catalyst deactivation due to the coordinate bonding of norbornene with a transition metal complex, it is possible to extend the distance between the polymerizable carbon-carbon double bonding and a polar group (ester group). For example, “J. Organomet. Chem., 2009, 694, p. 297-303” (Non-patent Document 1) discloses a case of producing a homopolymer of a nobornene compound wherein a one methylene chain is introduced between the norbornene skeleton and an ester group, having a number average molecular weight of 100,000 or more, by using N-heterocyclic carbene complex. However, the polymerization activity is very low in the method and the method failed to obtain a polymer having a number average molecular weight exceeding 200,000.
From the description of these prior art documents, it can be seen that a high-activity catalyst system capable of obtaining a copolymer having a number average molecular weight as high as 200,000 or more in addition polymerization of norbornene monomers alone containing polar groups or addition copolymerization of norbornene monomers containing polar groups, which system experiences little deactivation, was previously unknown.
As discussed above, in a method for producing addition (co)polymers of norbornene containing polar groups, there have been no previous cases of a high activity catalyst which enables obtaining a norbornene (co)polymer having practical mechanical properties. Consequently, development of such a catalyst has been demanded.